This multi-site study will conduct for tuberculosis (TB) among out-of- treatment injection during users (IDUs) recruited from three communities in the western U.S.: The San Francisco Bay Area, Portland and Denver. Specific research objectives are to determine: (1) The prevalence of Mycobacterium tuberculosis infection by region, gender, race/ethnicity, age and HIV-infection status; (2) The incidence of the new M. tuberculosis infection, as indicated by tuberculin skin test conversions; (3) Behavioral and demographic correlates of TB infection, including homelessness, incarceration and drug use patterns; (4) The prevalence of skin test anergy among IDUs, by HIV-status and level of immune suppression (as reflected in DC4+ lymphocyte count); and (4) Behavioral correlates of skin test anergy. All three sites in this proposal are currently conducting community-based studies of IDUs which include interviews and HIV-antibody testing; studies for TB will be integrated with these existing projects. Over the course of this three-year study, we will perform tuberculin skin tests with purified protein derivative (PPD) on 1633 IDUs who meet our inclusion criteria; all PPD-negative IDUs will have this result confirmed by receiving a booster skin test one month later. One hundred fifty-seven HIV-infected IDUs and a random sample of 314 HIV-negative IDUs will be evaluated for skin test anergy using two standard controls (dermatophyton and mumps); CD4+ lymphocyte counts will be determined on all HIV-positive subjects. All PPD-positive subjects will be referred for chest X-rays and other medical evaluation to determine if active tuberculosis is present and (if not) whether preventive antituberculous therapy is indicated. All PPD-negative IDUs will receive another tuberculin skin test after six months to follow-up to look for new M. tuberculosis infections. PPD-negative subjects from San Francisco will receive additional screening for TB after twelve and eighteen months of follow-up. In addition to meeting the research objectives described above, this study will establish a model for TB testing of IDUs and other difficult-to-access populations in community- based settings.